teach fish how to swim

Teach fish how to swim is an idiomatic expression derived from the Latin proverb {{lang|la|piscem natare doces}}. The phrase describes the self-sufficiency of those who know better how to do everything than the experts. It corresponds to the expression, "teaching grandmother to suck eggs".{{cite web|last=Belton|first=John Devoe|title=A Literary Manual of Foreign Quotations, Ancient and Modern|url=https://archive.org/stream/literarymanualof00beltrich#page/150/mode/2up|publisher=G. P. Putnam|accessdate=11 April 2018|location=New York|page=151|date=1891}} Erasmus attributed the origins of the phrase in his Adagia to Diogenianus.{{Cite book |last=Erasmus |first=Desiderius |author-link=Erasmus |title=Collected Works of Erasmus |publisher=University of Toronto Press |year=2005 |editor-last=Grant |editor-first=John N. |volume=35: Adages Ill iv 1 to IV ii 100 |location=Toronto |page=134 |translator-last=Drysdall |translator-first=Denis |isbn=0802036430}} Read online: {{Google books|J_P8xVdZzKsC|Erasmus (2005)|page=134}}; compare Ἰχθὺν νηχέσθαι διδάσκεις

A corollary idiomatic phrase is part of common usage in Chinese "{{lang|zh|{{linktext|班門弄斧}}}}"Muehl, Louis Baker et al. (1999). {{Google books|B0v-zKw1s0MC|Trading Cultures in the Classroom: Two American Teachers in China|page=18}}; [http://www.proz.com/kudoz/chinese_to_english/linguistics/906782-%B0%E0%C3%C5%C5%AA%B8%AB.html 班门弄斧]: display one's slight skill before an expert e.g. 在你面前班门弄斧,太不好意思了 (I'm making a fool of myself trying to show off before an expert like you)